The telephone system is frequently used for communicating data between a terminal or a personal computer (PC) and remote terminal or computer, which are linked by a modem at each end of the phone line. Data typed into a keyboard at one end of the link are usually displayed on a monitor screen as they are input to the modem. The modem converts the signal output from the computer to a format suitable for transmission over the relatively narrow bandwidth of a standard voice communication telephone line. The receiving modem converts the signal back to a signal that is input to the receiving terminal and is displayed on its monitor. Data files downloaded from magnetic disks or from the electronic memory of a computer are transmitted in a similar manner, usually without being displayed on the monitor of either the transmitting or the receiving device.
Using a PC as a data terminal is relatively expensive and requires that a significant amount of desktop space be devoted to the computer. In a data collection network of users requiring occasional transmission of only relatively short data messages, providing a PC for each user in the network just for data collection may not be justified. Since a conventional PC terminal includes features that may not be required by a user, such as a full keyboard and a floppy disk (or hard drive), elimination of these components from the data terminal greatly reduces the cost of a network comprising many such data terminals and the user space required for each terminal. Further economics of size and cost are achieved by using an alphanumeric display having only one to two lines of characters instead of a full screen monitor. In addition, the low cost data terminal may include a more efficient input device and another form of nonvolatile memory in place of the keyboard and magnetic disk storage devices used on a PC.
In a data collection network in which data transmitted by each user are standardized, a typical data message may comprise, for example, a predefined function code, followed by a number. To facilitate rapid data entry, a list of commonly used predefined function codes and numerical sequences (or the digits from 0-9) should be stored in a nonvolatile media that is readily available to the user for input to his terminal. The input device should facilitate rapid data entry, but eliminate operator errors that occur when data are entered on a keyboard. One solution to this problem is to store the data as an optically scanned bar code.
Universal product codes (UPC) are one form of a bar code that is well known and commonly used in commerce to identify a product. A clerk scanning a UPC imprinted on the label of a product with an optical sensor wand inputs the UPC encoded data for transmission to a central processor that maintains inventory and pricing data for the store. Since all the common alphanumeric characters are represented by a Code 39 bar code, it can readily be used to store other data besides product identification. A printed list of predefined bar codes can thus serve as a nonvolatile storage medium for data messages that are input with an optical sensing wand for transmission over a telephone line.
An alternative medium for storing relatively short data messages is a magnetic strip. Magnetic strips are frequently used on credit cards for storing an identification code that is transmitted to a remote data processor by a merchant to confirm a credit transaction. The merchant also enters numerical data, either on a key pad or verbally over the telephone. U.S. Pat. No. 3,571,799 discloses a credit authorization terminal including a magnetic strip reader and a keyboard intended for just such use. Prior art magnetic strip data input terminals are typically dedicated to input of specific kinds of data, such as a credit card number, and are not designed for general data collection use.
Besides enabling the user to input short data messages stored on a nonvolatile medium, it is desirable that a low-cost data terminal provide other functions. For example, it would be expedient to store data messages that are frequently transmitted in a nonvolatile memory within the data terminal, so that they can be readily recalled and transmitted. It would also be desirable to permit a receiving data processor in the data collection network to prompt the user of the data terminal for input of specific data, either verbally, or through a message that is transmitted over the telephone line as a data signal and shown on the display of the data terminal. In addition, the user of the data terminal may wish to enter a message on his terminal display panel indicating, for example, where he may be reached while away from his desk.
Communication between a plurality of data terminals at a given location using the installed phone system wiring is typically only possible if a data signal compatible with the phone system is used. Standards have been promulgated requiring that signals produced by devices connected to the telephone system conform to certain specifications (Part 68, FCC Rules). Data are normally communicated over the telephone system using some form of a variable frequency signal that conforms to these standards (e.g., CCITT V.22, Bell 103, and Bell 212A).
One type of signal compatible with the telephone system comprises dual tone variations. Signals based on the dual tone multiple frequency (DTMF) system are preferred on most telephone exchanges to the alternative pulse system for dialing a telephone number. The DTMF signals control switching gear that connect the dialing phone to another phone in the system. Although DTMF signals are normally not used to convey characters other than the numbers 0-9, # and *, they can be used to convey a full range of alphanumeric data by combining them in specific combinations. Data transmission using DTMF signals is inherently slow, on the order of from three to ten characters per second. Modems communicate at much higher rates using quadrature amplitude modulation, differential phase shift keying, or frequency shift keying. However, the circuits to implement these schemes are somewhat expensive. Although the low data transfer rate of DTMF signals may be adequate for short data messages, a higher data communication rate may sometimes be preferred. It may also be desirable to use a signal which is not generally compatible with the requirements of the telephone system, such as a varying DC polarity, for communication between local terminals. Conventional data terminal systems generally do not include any provision for communication over installed local phone lines, other than by using telephone system compatible signals.
In consideration of the features and functions desired of the data terminal and data collection network described above, which are not provided by the prior art, it is an object of the present invention to provide a compact, relatively low cost data terminal for use in a data collection network to communicate data over a telephone system that uses DTMF tone dialing. It is a further object of the invention to store data in the data terminal, within nonvolatile memory, for selective recall and transmission.
Yet another object is to provide means for the data terminal to receive a prompt message from a remote data processor, requesting specific data be transmitted. A still further object is for the data terminal to communicate data over a local telephone line to other local data terminals or a data processor, using signals that are incompatible for use on the telephone system. These and other objects and advantages of the present invention will be apparent from the attached drawings and from the Description of the Preferred Embodiment that follows.